1. Field of the Invention
This invention relates generally to image forming apparatus in which each image frame is regarded as an aggregate of geometric image areas, and which particularly deals with videotex codes consisting of sequential codes composed of geometric codes which represent individual image areas as respective geometric drawings, and also characteristic or attribute codes representing attributes of the geometric drawings.
2. Related Application
U.S. Patent Application Serial No. 06/713,612, filed Mar. 19, 1985, by persons having a duty to assign to the assignee of the present application, and which is in fact assigned to said assignee, discloses subject matter related to the present application, and such disclosure is incorporated herein by reference Application Ser. No. 06/713,612 issued Feb. 24, 1987, as U.S. Pat. No. 4,646,134.
3. Description of the Prior Art
Digital image information transmitting systems for transmitting videotex and teletext information have been developed and used in various countries as new media of transmission of various kinds of image information via telephone circuits and radio waves. For example, a CAPTAIN PLPS system has been developed in Japan on the basis of the CAPTAIN (Character and Pattern Telephone Access Information Network) system, a NAPLPS (North American Presentation-Level-Protocl Syntax) system has been developed as a modification of the TELIDON system in Canada and is now the standard system for North American and a CEPT PLPS system has been developed in England based on the PRESTEL system.
In the NAPLPS system, each image frame is handled as an aggregate of geometric image areas, and videotex codes consisting of sequential codes composed of geometric codes representing individual image areas as respective geometric drawings and characteristic or attribute codes representing characteristics or attributes of the geometric drawings are transmitted. This system is highly rated as having a very high transmission efficiency as compared to other systems in which image information is made to correspond to mosaic picture elements, or systems in which image information is represented by other character codes.
In the NAPLPS system, five different geometric or PDI (Picture Description Instruction) codes, namely the codes [POINT], [LINE], [ARC], [RECTANGLE] and [POLYGON] are employed as basic geometric drawing commands. There are also characteristic or attribute codes which specify the logical pel size or line thickness, color and texture, respectively, of the geometric drawings formed according to the geometric codes, and codes specifying the operands (coordinate values) which define the positions on a viewing screen of the drawings formed according to the geometric codes.
In the NAPLPS system, the geometric or PDI codes, the characteristic or attribute codes and the codes representing the operands are transmitted in a predetermined time sequence, for example, in the order, characteristic or attribute codes for pel size, color and texture, PDI codes and then operand codes, with the attribute and PDI codes appearing in the sequence only when there is a change therein. Therefore, when transmitting digital image information in accordance with the NAPLPS system, the amount of image information transmitted can be greatly reduced, that is, a high image information transmission efficiency can be obtained. However, the information specified by any one of the geometric or PDI codes is incomplete and the definition of the respective geometric image area further requires the respective characteristic or attribute codes and operand codes. Therefore, alternations of the order or nature of the geometric codes or of the characteristic or attribute codes require very complicated operations. This means that a great deal of time is required for producing one frame of image information to be transmitted.
An image formed using the videotex code data noted above, can be advantageously expressed in various ways, for example, by overlaying one drawing over another drawing. As an example of the foregoing, a drawing of a bird may be overlaid upon a drawing of a sky with clouds or other suitable background, and the bird will appear to be in flight if the drawing thereof is periodically and suitably changed in its contours and/or colors. However, as noted before, the information specified by the geometric codes and also the data of the characteristic codes and operands are required for defining the image, so that alterations in the order of the geometric codes and/or alterations of the characteristic codes require very complicated operations, making it necessary to expend a great deal of time for producing each frame of the image information to be transmitted. It is particularly very difficult to select for alteration an underlying drawing concealed by an overlying drawing of an image composed of overlaying drawings, and to collect the selected drawing for its alteration or correction.
Further, when image information based on videotex codes is to be formed from a color video signal obtained by viewing with a video camera an original color image to be transmitted, a great deal of unnecessary or redundant information about the color hue, gradation, and the like is obtained. Such redundant information must be adequately reduced to a quantity suited for the data based on the videotex codes without sacrificing desired features of the original color image represented by the video signal.
Further, when character fonts and texture patterns are defined by the user, the defined character fonts and texture patterns must be accurately read out at the receiving side of the system. This indicates the need for providing information services corresponding to the functions of the apparatus at the receiving side of the system.